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United States Patent |
5,735,248
|
Matsuura
,   et al.
|
April 7, 1998
|
Fuel injection method for gas fuel engine
Abstract
A fuel injection method wherein optimum fuel injection timing in a
fuel-injection type gas fuel engine is determined by setting fuel
injection end timing to be after the start of opening of an intake valve.
That is, when injection ends in a first half of the intake valve open
period the volumetric efficiency .eta.v falls and the engine output also
falls, because the injection period overlaps with a period of positive
pressure arising inside the intake pipe before opening of the intake
valve, but when injection ends in a second half of the intake valve open
period the volumetric efficiency .eta.v rises and the engine efficiency
also rises, because the injection period overlaps with a period of
negative pressure arising in the intake pipe during the first half of the
intake value open period. Consequently, when fuel is injected during this
trough in the intake port pressure, the volumetric efficiency increases
and the engine output also increases by several percent.
Inventors:
|
Matsuura; Hiromi (Wako, JP);
Minami; Hideki (Wako, JP);
Nakajima; Susumu (Wako, JP);
Ueda; Kazuhiro (Wako, JP);
Aoki; Shigeru (Wako, JP);
Nishida; Toshiyuki (Wako, JP)
|
Assignee:
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Honda Giken Kogyo Kabushiki Kaisha (Tokyo, JP)
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Appl. No.:
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698519 |
Filed:
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August 15, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
123/527; 123/478 |
Intern'l Class: |
F02M 021/02 |
Field of Search: |
123/478,526,527,528,DIG. 12
|
References Cited
U.S. Patent Documents
3125085 | Mar., 1964 | Kaufmann | 123/527.
|
4505249 | Mar., 1985 | Young | 123/527.
|
5203305 | Apr., 1993 | Porter et al. | 123/527.
|
5329908 | Jul., 1994 | Tarr et al. | 123/527.
|
5477830 | Dec., 1995 | Beck et al. | 123/478.
|
5487362 | Jan., 1996 | Wellev et al. | 123/526.
|
5533492 | Jul., 1996 | Willey et al. | 123/527.
|
5553575 | Sep., 1996 | Beck et al. | 123/198.
|
Foreign Patent Documents |
2 304 767 | Aug., 1974 | DE.
| |
59-138763 A | Aug., 1984 | JP.
| |
133562 | Jun., 1929 | CH.
| |
WO 94/13946 | Jun., 1994 | WO.
| |
Other References
Lynch, "Parallel Induction: A Simple Fuel Control Method for Hydrogen
Engines", Int. J. Hydrogen Energy, vol. 5, No. 9, 1 Sep. 1983, Norwich,
Great Britain, pp. 721-730.
Peschka, Liquid Hydrogen Fueled Automotive Vehicles in Germany--Status and
Development, Int. J Hydrogen Energy, vol. 8, No. 9, 1 Nov. 1986, Norwich,
Great Britain, pp. 721-728.
|
Primary Examiner: Argenbright; Tony M.
Attorney, Agent or Firm: Merchant, Gould, Smith, Edell, Welter & Schmidt, P.A.
Claims
What is claimed is:
1. A fuel injection method for a gas fuel engine having an intake port into
which a gaseous fuel is injected, said method comprising the step of:
setting fuel injection end timing to be after the start of opening of an
intake valve of said engine and fuel injection start timing to be before
the start of opening of said intake valve of said engine.
2. A fuel injection method according to claim 1, further comprising the
steps of:
causing ignition to take place at a crank angle of 0.degree. and at a top
dead center; and
causing fuel injection to end at a crank angle in a range of
480.degree.-690.degree..
3. A fuel injection method for a gas fuel engine having an intake port into
which a gaseous fuel is injected, said method comprising the steps of:
causing the injection to take place at a plurality of divided injection
periods; and
making said injection periods coincide with periods in which intake port
pressure falls in the shape of a trough.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel injection method for a gas fuel
engine.
2. Description of the Related Art
As substitutes for gasoline engines in which gasoline is used as fuel and
for diesel engines in which light oil is used as fuel, gas fuel engines
using natural gas (hereinafter abbreviated as NG) or LPG as fuel have come
into use. Fuel supply systems in these gas fuel engines include the
following types:
(a) Firstly, there is a fuel supply system of "Gas Fuel Engine" disclosed
in Japanese Patent Laid-Open Publication No. SHO 59-138763. In this
system, a mixer is provided in place of the carburetor used in a gasoline
engine, and low-pressure fuel gas and a suitable quantity of air are mixed
by this mixer. This mixer method is presently widely used mainly in taxis.
(b) Secondly, there are fuel supply systems using the fuel injection
method. This fuel injection method is one wherein fuel injection
technology employed in diesel engines and gasoline engines is applied and
suitable quantities of gaseous fuel are injected into an intake manifold.
This injection of gaseous fuel is performed by injectors, and the optimum
value of the quantity of fuel injected is calculated by an ECU (Electronic
Control Unit) on the basis of information such as the engine speed, the
negative pressure (the intake negative pressure) arising in the intake
system, the throttle angle, the engine cooling water temperature and the
concentration of oxygen in the exhaust gas.
A graph showing an example of the fuel injection timing of a conventional
gasoline engine is shown in FIG. 13. The horizontal axis is injection end
timing and is shown by crank angle.
In a gasoline engine, for reasons such as that because when fuel is
injected while the intake valve is open it is not possible to secure
sufficient time for evaporation of the liquid fuel and that consequently
mixing tends to be incomplete, fuel is generally injected avoiding the
period during which the intake valve is open. Accordingly, as shown in
FIG. 13, if the intake valve is open for a crank angle of about
370.degree. to about 570.degree., fuel injection is for example started at
crank angle 180.degree. and ended at crank angle 270.degree..
Now, for NG and for gasoline mist the volume of fuel per unit heat produced
is greatly different. With respect to a volume of 1.0 for gasoline, the
corresponding volume of NG is 600. Thus, in the case of NG, the volume of
fuel is larger.
A graph showing an example of the fuel injection timing of a conventional
gas fuel engine is shown in FIG. 14 and corresponds to FIG. 13. Because
the volume of fuel is much larger, as explained above, the fuel injection
time in this example has a width in terms of crank angle of about
200.degree., with fuel injection starting at crank angle 70.degree. and
ending at crank angle 270.degree..
In the mixer method (a) described above, the mixer is a type of throttle
mechanism having a venturi or the like, and a pressure loss occurs in
proportion with the degree of the throttling. Because of this, the amount
of intake air decreases and the volumetric efficiency .eta.v falls. When
to avoid this problem the mixer and the intake manifold are increased in
size, besides enlargement of the engine space and the vehicle becoming
large due to the engine becoming large, there is an adverse affect on the
output characteristics of the engine and on fuel combustion in the partial
load region, and therefore from the points of view of fuel consumption,
emissions and driveability this is not a preferable solution.
In the fuel injection method (b) described above, there are none of the
above-mentioned adverse affects caused by throttling. However, in the case
of NG the proportion of the volume of the fuel/air mixture occupied by the
fuel reaches 10% and in the case of H.sub.2 the proportion of the volume
of the fuel/air mixture occupied by the fuel reaches 30%. The proportion
of intake air in the mixture decreases by an amount corresponding to the
increase in the volume of the fuel, and compared to a gasoline engine or a
diesel engine the amount of intake air decreases and the volumetric
efficiency .eta.v falls.
Also, the above-mentioned fuel injection method is based on gasoline engine
fuel injection technology, as shown in FIG. 14, and there are aspects
wherein factors peculiar to NG are not fully taken into account,
specifically the matter of the fuel volume and the fact that evaporation
is not necessary.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a fuel
injection method with which it is possible to establish a gas fuel engine
matched to factors peculiar to NG and to obtain a predetermined volumetric
efficiency .eta.v without greatly enlarging an existing engine.
In a fuel injection method according to a first aspect of the invention,
the fuel injection end timing is set to after the start of opening of the
intake valve. Because the injection period therefore overlaps with a
period over which a negative pressure arises inside the intake pipe during
the first half of the period for which the intake valve is open, the
volumetric efficiency .eta.v increases and the engine output also
increases by several percent.
In a fuel injection method according to a second aspect of the invention,
top dead center and ignition are at crank angle 0.degree. and the fuel
injection end timing is set so as to be in the range of crank angle
480.degree. to 690.degree.. As a result, in the range of crank angle
480.degree. to 690.degree. the knock margin is greater than at other
times, and by setting the fuel injection end timing in this range it is
possible to stabilize fuel combustion and increase volumetric efficiency
and engine output.
In a fuel injection method according to a third aspect of the invention,
the overall injection is carried out divided into a plurality of separate
smaller injection periods, and these injection periods are made to
coincide with periods during which the intake port pressure falls in the
shape of a trough. Because the injection period overlaps with a period
over which a negative pressure arises inside the intake pipe during the
first half of the period for which the intake valve is open, the
volumetric efficiency .eta.v increases and the engine output also
increases by several percent. Also, because the injection period sometimes
extends beyond the period of this trough during high-load running at which
time a large quantity of fuel is consumed, if fuel injection is carried
out in a plurality of divided small injection periods, it can be kept in
the troughs, whereby high output can be obtained during high-load running.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention will hereinafter be described in
more detail, by way of example, with reference to the accompanying
drawings, in which:
FIG. 1 is a schematic view showing the disposition in a vehicle of a fuel
supply system of a gas fuel engine;
FIG. 2 is a view showing in detail a fuel supply system of a gas fuel
engine;
FIG. 3A and FIG. 3B are views showing layouts of devices disposed around an
intake manifold;
FIG. 4A and FIG. 4B are views showing layouts of devices disposed around an
intake manifold;
FIG. 5A and FIG. 5B are graphs showing basic data obtained using a gas fuel
engine;
FIG. 6 is a waveform graph of pulsation inside an intake port of an example
(First Preferred Embodiment) wherein single-stage injection was carried
out at an engine speed of 4000 rpm;
FIG. 7 is a waveform graph of pulsation inside an intake port in an example
(Second Preferred Embodiment) wherein multi-stage injection was carried
out at an engine speed of 4000 rpm;
FIG. 8 is a graph comparing the first and second preferred embodiments of
the invention with a first comparison example;
FIG. 9 is a waveform graph of pulsation inside an intake port in an example
(third preferred embodiment) wherein single-stage injection was carried
out at an engine speed of 6600 rpm;
FIG. 10 is a waveform graph of pulsation inside an intake port in an
example (Fourth Preferred Embodiment) wherein multi-stage injection was
carried out at an engine speed of 6600 rpm;
FIG. 11 is a graph comparing the third and fourth preferred embodiments of
the invention with a second comparison example;
FIG. 12 is a graph showing a relationship between injection end timing and
knock margin;
FIG. 13 is a graph showing an example of conventional fuel injection timing
of a gasoline engine; and
FIG. 14 is a graph showing an example of conventional fuel injection timing
of a gas fuel engine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, two tanks 1, 2 containing NG at a high pressure of for example
200 Kg/cm.sup.2 are mounted in a trunk space in the rear of a vehicle and
a water-cooled gas engine 10 is mounted in the front of the vehicle.
A high-pressure pipe 6 for carrying high-pressure gas from inside the tanks
1, 2 to the gas engine 10 side is mounted below the cabin in the middle of
the vehicle. A primary pressure regulator 8 as a pressure-reducing device
for reducing the pressure of the gas carried by the high-pressure pipe 6
to, for example, about 7 Kg/cm.sup.2 and a secondary pressure regulator 9
for further reducing the pressure of this pressure-reduced gas to, for
example, about 2 Kg/cm.sup.2 by gauge pressure are disposed in the engine
space in the front of the vehicle.
The gas reduced in pressure by the secondary pressure regulator 9 is
injected into cylinders of the engine 10 through a plurality of injectors
12 and is discharged through a catalytic convertor 14 of the exhaust
system of the engine 10.
In FIG. 2, a tank pipe 22 is disposed between the two tanks 1, 2 and a fuel
filling opening 20. A nonreturn valve 22a is provided in this tank pipe 22
to prevent back flow of filled gas, and downstream of this a tank gas
detecting part 5 is provided as a part connecting the tank pipe 22 to
high-pressure pipes 3, 4.
A temperature sensor 19 for measuring the tank gas temperature and a
pressure sensor 21 for detecting the tank gas pressure are provided in the
tank gas detecting part 5.
First magnetic cutoff valves 15, 16 are provided in inlet openings of the
tanks 1, 2 respectively, and these first magnetic cutoff valves 15, 16 are
controlled to open and close by an ECU (Electronic Control Unit). Also,
relief valves 17, 18 are provided at the opposite ends of the tanks 1, 2
respectively.
A manual valve 25, which can be opened and closed by hand, is provided in
the upstream side of the high-pressure pipe 6 and a filter 30 is provided
in the downstream side. A second magnetic cutoff valve 7 is provided
between the filter 30 and the primary pressure regulator 8, and this
second magnetic cutoff valve 7 is controlled to open and close by the ECU.
The primary pressure regulator 8 is provided with a water passage 31
through which can be passed cooling water having circulated around the
engine 10.
A primary gas detector part 32 having a primary pressure sensor 33 is
disposed downstream of the primary pressure regulator 8. This primary gas
detector part 32 is provided with a relief valve 34, and a relief pipe 40
(see FIG. 1) is connected to the relief valve 34.
The secondary pressure regulator 9 is disposed downstream of the primary
gas detector part 32, and the gas pressure of the gas finally supplied to
the engine 10 is pressure-regulated by this secondary pressure regulator
9.
Gas precisely pressure-regulated by the secondary pressure regulator 9 is
fed through a low-pressure pipe 26 into an intake manifold 11 and injected
through intake ports 13 into the cylinders of the engine 10 by the
injectors 12. The injection method in this preferred embodiment is the
multi-point injection (MPI) method wherein a plurality of injectors 12 are
provided in one-to-one correspondence with the cylinders. Reference
numerals 10a and 10b designate an intake valve and an exhaust valve,
respectively.
A secondary temperature sensor 23 for detecting a secondary gas temperature
and a secondary pressure sensor 24 for detecting a secondary gas pressure
are provided inside the intake manifold 11, and detection signals from
these sensors are fed to the ECU, which limits the fuel injection. The ECU
also takes into account other data of the engine 10 and carries out fuel
injection control by driving an injection driver.
An inertia switch 29 is disposed below the steering wheel inside the
passenger compartment of the vehicle. The inertia switch 29 is disposed
together with a normally open relay R in a wiring line connecting an
ignition switch 28 to the ECU. When the ignition switch 28 and the inertia
switch 29 are ON (normal), the normally open relay R is closed, current is
passed through the first magnetic cutoff valves 15, 16 and the second
magnetic cutoff valve 7, and the first magnetic cutoff valves 15, 16 and
the second magnetic cutoff valve 7 are thereby opened. When either the
ignition switch 28 or the inertia switch 29 is OFF, the first magnetic
cutoff valves 15, 16 and the second magnetic cutoff valve 7 are closed.
Reference number 27 indicates a pressure sensor for detecting pressure
pulsation, and a detection signal thereof is inputted into the ECU.
Reference number 35 indicates a throttle valve.
The ECU, on the basis of information from the temperature sensor 19, the
pressure sensor 21, the secondary temperature sensor 23 and the secondary
pressure sensor 24, executes steps such as, for example, closing the
second magnetic cutoff valve 7 when the pressure has fallen below a
certain level.
Layouts of devices disposed around the intake manifold 11 are shown in FIG.
3A and FIG. 3B.
In the device layout shown in FIG. 3A, the second magnetic cutoff valve 7,
the primary pressure regulator 8, the secondary pressure regulator 9, the
intake manifold 11 and the plurality of injectors 12 are disposed along
the flow of the fuel. Because the distance from the second magnetic cutoff
valve 7 to the intake manifold 11 is relatively large, as shown in FIG. 2,
even if the second magnetic cutoff valve 7 has been closed, fuel collected
between the second magnetic cutoff valve 7 and the intake manifold 11
leaks out through the injectors 12.
In FIG. 3B, a third magnetic cutoff valve 36 has been added on the upstream
side of the intake manifold 11, and by this third magnetic cutoff valve 36
being closed when necessary, it is possible to hold fuel on the upstream
side of the third magnetic cutoff valve 36 and the amount of fuel leaking
from the injectors 12 decreases correspondingly.
FIG. 4A and FIG. 4B show other examples of layouts of devices disposed
around the intake manifold 11.
FIG. 4A shows an example wherein third magnetic cutoff valves 36 are
interposed between the intake manifold 11 and each of the injectors 12.
FIG. 4B shows an example wherein third magnetic cutoff valves 36 are
integrally built into the injectors 12.
Thus, in both of the examples shown in FIG. 4A and FIG. 4B, the amount of
fuel leaking from the injectors 12 decreases.
Using the apparatus described above, collection of basic data and the
method of the present invention were carried out.
FIG. 5A and FIG. 5B are basic data graphs obtained using a gas fuel engine;
the horizontal axis shows timing by crank angle (.degree.), and the
vertical axis is volumetric efficiency .eta.v or engine output. The
exhaust valve open period and the intake valve open period are as shown in
FIG. 5A. The engine speed is 4000 rpm, and the throttle valve 35 (see FIG.
2) was made fully open.
In FIG. 5A, for example the volumetric efficiency .eta.v obtained when
injection was carried out with the conditions that the injection period
was given a width in terms of crank angle of 240.degree. and the injection
end timing was 300.degree., as shown by c, was shown by a circle d.
Similarly for the other circles, the injection end timing was shifted by
30.degree. at a time and the volumetric efficiency .eta.v was obtained,
its value at that time was shown by a circle and the circles were joined
together with straight lines. From this graph a large trough can be seen
in the vicinity of crank angle 450.degree..
The horizontal line e is the average value of the volumetric efficiency
.eta.v over the range of crank angle 0.degree. to 450.degree.. When this
horizontal line e is extended, a range of at least 480.degree. to
690.degree. is above this average.
Focusing on this 450.degree. to 480.degree. range, this 450.degree. to
480.degree. range lies in the middle of the intake valve open period, and
before this range the volumetric efficiency .eta.v is decreasing and after
this range it is increasing. Consideration of this yields the following:
In a case where injection ends in the first half of the intake valve open
period: because the injection period overlaps with a period of positive
pressure arising inside the intake pipe before opening of the intake
valve, the volumetric efficiency .eta.v falls and output also falls.
In a case where injection ends in the second half of the intake valve open
period: because the injection period overlaps with a period of negative
pressure arising inside the intake pipe during the first half of the
intake valve open period, the volumetric efficiency .eta.v rises and
output also rises.
Accordingly, the present inventors discovered that it is possible to raise
volumetric efficiency .eta.v and output by performing injection
concentrated in a trough part of the intake port pressure pulsation.
FIG. 5B is a graph of engine output plotted by the same method; it
substantially approximates to the curve of FIG. 5A, and a large trough can
be seen in the vicinity of crank angle 450.degree..
Preferred Embodiments
Preferred embodiments of the invention will now be described.
FIG. 6 shows a waveform chart of a pulsation inside an intake port in an
example (a first preferred embodiment) wherein single-stage injection was
carried out at an engine speed Ne of 4000 rpm; the horizontal axis is
crank angle and the vertical axis is intake port pressure; on the
horizontal axis TDC is Top Dead Center and BDC is Bottom Dead Center.
Ignition is at 0.degree. (and similarly below).
In the first preferred embodiment, to cover the large trough in the intake
port pressure at 450.degree., injection was started at crank angle
340.degree. and injection was ended at crank angle 560.degree..
FIG. 7 shows a waveform chart of a pulsation inside an intake port in
another example (a second preferred embodiment) wherein multi-stage
injection was carried out at an engine speed Ne of 4000 rpm; the
horizontal axis is crank angle and the vertical axis is intake port
pressure.
In the second preferred embodiment, to cover the trough at 280.degree. and
the large trough at 450.degree., first injection was started at crank
angle 240.degree. and ended at crank angle 350.degree. and then injection
was started again at crank angle 400.degree. and ended at crank angle
515.degree..
In this second preferred embodiment, because the overall injection which,
in the above-mentioned FIG. 5, was completed with a single injection was
divided into two injections, the injection time per injection naturally is
smaller.
As is clear from FIG. 7, injection may be carried out in the trough around
crank angle 110.degree. also, and injection may be performed in any
suitable number of stages.
A graph comparing the first and second preferred embodiments of the
invention and a first comparison example is shown in FIG. 8; the vertical
axis is engine output.
The first comparison example is the output in a case where injection was
carried out under the conditions shown in FIG. 14, the first preferred
embodiment is the output obtained with the single-stage injection shown in
FIG. 6 and the second preferred embodiment is the output obtained with the
multi-stage injection (two-stage injection) shown in FIG. 7.
If the comparison example is made 100, the first preferred embodiment is
102 and the second preferred embodiment is 103, and output increases of 2%
and 3% respectively were achieved.
FIG. 9 shows a waveform chart of a pulsation inside an intake port a third
example (a third preferred embodiment) wherein single-stage injection was
carried out at an engine speed Ne of 6600 rpm; the horizontal axis is
crank angle and the vertical axis is intake port pressure. In this third
preferred embodiment, to cover the large trough at 450.degree., injection
was started at crank angle 260.degree. and injection was ended at crank
angle 630.degree..
FIG. 10 shows a waveform chart of a pulsation inside an intake port in a
fourth example (a fourth preferred embodiment) wherein multi-stage
injection was carried out at an engine speed Ne of 6600 rpm; the
horizontal axis is crank angle and the vertical axis is intake port
pressure.
In this fourth preferred embodiment, to cover the trough at 180.degree. and
the large trough at 450.degree., first injection was started at crank
angle 80.degree. and injection was ended at crank angle 270.degree. and
then injection was started again at crank angle 400.degree. and ended at
crank angle 595.degree..
FIG. 11 shows a graph comparing the third and fourth preferred embodiments
of the invention and a second comparison example, the vertical axis being
engine output.
The second comparison example is the output in a case where injection was
carried out under the conditions shown in FIG. 14, the third preferred
embodiment is the output obtained with the single-stage injection shown in
FIG. 9 and the fourth preferred embodiment is the output obtained with the
multi-stage injection (two-stage injection) shown in FIG. 10.
If the second comparison example is made 100, the third preferred
embodiment is 100.4 and the fourth preferred embodiment is 102, and output
increases of 0.4% and 2% respectively were achieved.
FIG. 12 is a graph showing a relationship between injection end timing and
knock margin; the horizontal axis shows injection end timing by crank
angle and the vertical axis is knock margin (.degree.), defined below. The
circles in the graph are injection end points similar to those in FIG. 5.
knock margin=knock occurrence angle-MBT
The knock occurrence angle and the MBT are crank angles BTDC (before top
dead center). The MBT (Minimum advance for the Best Torque) is the
ignition timing giving the best engine output, fuel consumption rate.
The greater the knock margin is, the less readily the knocking phenomenon
occurs. Because the knock margin is large in the range of crank angle
420.degree. to 690.degree., and especially in the range of 480.degree. to
630.degree., injection should be controlled so that injection ends in this
range.
The range of 480.degree. to 690.degree. in FIG. 5 can also be explained
from the point of knock margin (preferable range 420.degree. to
690.degree.). Therefore, the preferable injection end timing in this
invention is made the range of 480.degree. to 690.degree..
To control the above-mentioned injection period, in FIG. 2, information
from the engine 10 such as the engine speed, the throttle valve secondary
side pressure, the crank angle, the concentration of oxygen in the
exhaust, a crank pulse, a TDC pulse and cylinder identification signals
are fed to the ECU. The ECU has stored in ROM injection timing calculation
formulas and tables and maps or the like corresponding to engine speed and
throttle valve secondary side pressure; it calculates injection timing
based on this information and controls injector driving currents of the
cylinders or an injector driver driving current.
The pulsation waveform is read out by the pulsation pressure sensor 27, and
the crank angle of the lowest part (the bottom of the trough) of the
pulsation waveform during the intake valve open period is calculated.
When the injection end timing computed from the various signals exceeds
crank angle 690.degree., the injection period is shifted forward to deal
with this.
The control procedure described above is only an example, and this
procedure and the number and types of the items of information used for
realizing the method of the invention may be changed.
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